1. Technical Field
The present invention relates to apparatus for biologic fluid analyses in general, and to cartridges for acquiring, processing, and containing biologic fluid samples for analysis in particular.
2. Background Information
Historically, biologic fluid samples such as whole blood, urine, cerebrospinal fluid, body cavity fluids, etc. have had their particulate or cellular contents evaluated by smearing a small undiluted amount of the fluid on a slide and evaluating that smear under a microscope. Reasonable results can be gained from such a smear, but the cell integrity, accuracy and reliability of the data depends largely on the technician's experience and technique.
Another known method for evaluating a biologic fluid sample involves diluting a volume of the sample, placing it within a chamber, and manually evaluating and enumerating the constituents within the diluted sample. Dilution is necessary if there is a high concentration of constituents within the sample, and for routine blood counts several different dilutions may be required because it is impractical to have counting chambers or apparatus which can examine variable volumes as a means to compensate for the disparities in constituent populations within the sample. In a sample of whole blood from a typical individual, for example, there are about 4.5×106 red blood cells (RBCs) per microliter (μl) of blood sample, but only about 0.25×106 of platelets and 0.007×106 white blood cells (WBCs) per μl of blood sample. To determine a WBC count, the whole blood sample must be diluted within a range of about one part blood to twenty parts diluent (1:20) up to a dilution of approximately 1:256 depending upon the exact dilution technique used, and it is also generally necessary to selectively lyse the RBCs with one or more reagents. Lysing the RBCs effectively removes them from view so that the WBCs can be seen. To determine a platelet count, the blood sample must be diluted within a range of 1:100 to about 1:50,000. Platelet counts do not, however, require a lysis of the RBCs in the sample. Disadvantages of evaluating a whole blood sample in this manner include the dilution process is time consuming and expensive, increased error probability due to the diluents within the sample data, etc.
Another method for evaluating a biologic fluid sample is impedance or optical flow cytometry, which involves circulating a diluted fluid sample through one or more small diameter orifices, each employing an impedance measurement or an optical system that senses the different constituents in the form of scattered light as they pass through the hydrodynamically focused flow cell in single file. In the case of whole blood, the sample must be diluted to mitigate the overwhelming number of the RBCs relative to the WBCs and platelets, and to provide adequate cell-to-cell spacing and minimize coincidence so that individual cells may be analyzed. Disadvantages associated with flow cytometry include the fluid handling and control of a number of different reagents required to analyze the sample which can be expensive and maintenance intensive.
Another modern method for evaluating biologic fluid samples is one that focuses on evaluating specific subtypes of WBCs to obtain a total WBC count. This method utilizes a cuvette having an internal chamber about 25 microns thick with one transparent panel. Light passing through the transparent panel scans the cuvette for WBCs. Reagents inside the cuvette cause WBCs to fluoresce when excited by the light. The fluorescing of the particular WBCs provides an indication that particular types of WBCs are present. Because the red blood cells form a partly obscuring layer in this method, they cannot themselves be enumerated or otherwise evaluated, nor can the platelets.
What is needed is a method and an apparatus for evaluating a sample of substantially undiluted biologic fluid, one capable of providing accurate results, one that does not use a significant volume of reagent(s), one that does not require sample fluid flow during evaluation, one that can perform particulate component analyses, and one that is cost-effective.